Well the Nikkor 50 f1.8g is difficult to compete with on that price level since its almost 4 times cheaper than the Zeiss 50 f2 Macro (which is the best for shapness).

If you take only price and sharpness in to consideration then the 50 f1.8g offers the best value hands down.

What you gain by going up-price is mostly build quality mainly the zeiss and Voightlander are very nicely put togther. the Nikkor 50 f1.4 is very similar to the 1.8. You also gain a little in IQ but its marginal since all 50mm are in general very good.